Andreas, the first thing to remember is that this paint is very thin and covers supremely well with jus' one coat, even over black. You don't need to work the paint around for fear of leavin' any brush marks, its impossible to leave brush marks in this stuff, 'cos of its thinness.
I always 'cut' or edge in the area first that needs to be painted, then with a slightly larger brush fill in the rest of the area with paint. I always apply a second coat for maximum effect.
I only use a matt black automotive paint as a primer, which dries to a slight satin finish which is totally totally smooth, but still has some 'tooth' to take the paint. As a result, when these alc-based paints are applied, they're totally flat and smooth, too.
I'm not so sure about some of these rough or gritty primers, the majority of which need to be sanded smooth, anyway.
I say this 'cos these paints are very thin.
Preperation is the key with this paint.
This paint is permanent, you can never rub it off unless you care to scrape away the white metal.